Damaging Mechanism Of Space Charged Particles Radiation For GeAs/Ge Solar Cells

At present, main works about electrical performance degradation of the solar cells aretest and theory. Deep level transient spectrum test is meaningful method, which cananalyze the defect types, concentration and capture cross section, but can’t gave howthese defects affect the solar cells. The work about theory is mainly to establish a cellmodel, and give the regression equation of the open circuit voltage and short circuitcurrent. Because the model is so simplified that ignoring many factors which couldinfluence the electrical performance of the cell, further research needs still. In addition,most of the works for process simulations are the application of SRIM and CASINOprograms for materials(not devices) simulating to give qualitative damage of cells Mostof works can’t well reveal the internal damage process of cells and the variation ofparameters which could lead to the electrical performance degradation of cells isn’tgiven.Spectral response and the I-V characteristic by irradiation of electrons and protons arecarried out for domestic GaAs/Ge solar cells. Quantum efficiency curves of GaAs/GeSolar cells are reproduced by PC1D program. The relevant parameters of the GaAs/Gesolar cells before and after irradiation are obtained. The battery internal damage processand electrical performance degradation mechanism are revealed by the parametervariations of GaAs/Ge solar cells.Firstly, the parameters of GaAs/Ge solar cells are obtained through the PC1D processto reproduce quantum efficiency before after irradiation, including the minority carrierlifetime for0.3us, the front surface recombination rate of5×104cm/s and rear surfacerecombination rate of4×104cm/s.Secondly, result quantum efficiency of GaAs/Ge solar cells for1MeV electronirradiation by PC1D process simulation shows that the damage to the cell is uniform by1MeV electron irradiation. Photoproduction Minority carrier diffusion length in thebase region changes from9um for initial to0.94um for1x1015cm-2electronirradiation.Majority carrier concentration in the base varies from2x1017cm-3to7x1016cm-3. Diffusion length damage coefficient of minority carrier(KL) in the baseregion is1.076x10-7; Removal rate of majority carrier(RC) in the base210.42cm-1. Declining of minority carrier diffusion length after1MeV electron irradiation is themain factor to the degradation of short-circuit current for cells；Removing effect is oneof the reasons for the degradation of open circuit voltage.Thirdly, the result of quantum efficiency of GaAs/Ge solar cells for high-energyprotons irradiation by PC1D process simulation shows that this damage mechanism issimilar to1MeV electron irradiation, but the degree of injury. The majority carrierremoval rates are in the base region2.1×104cm-1and1.6×104cm-1irradiated by4Mevand10MeV protons. Diffusion length damage coefficients were2.6×10-4and1.9x10-4.The damage degree irradiated by4MeV protons is greater than by the10MeV protonsand the damage degree radiated by1MeV electrons is lower than the by high-energyprotons.Finally, the result of quantum efficiency of GaAs/Ge solar cells for low-energyelectron irradiation by PC1D process simulation shows that40keV and170keV protonsirradiation cause injury of emitter and base region for cells.The damage mechanismirradiated by40keV and170keV protons is similar to high-energy protons irradiation.The minority carrier lifetime in the emitter irradiated by40keV protons degradesseverely to3×10-6at fluences of5×10cm2.The diffusion length is much less than thethickness of the emitting region, resulting in severe recession of short-circuit current.The majority carrier removal rate in the emitter region is2.063×106cm-1. The majoritycarrier removal rate in the base region irradiated by170keV protons is3.29×106cm-1and the diffusion length damage coefficient is6.08×10-3. I-V characteristics irradiatedby70keV and100keV protons through PC1D program are different with theexperimental results, because that70keV and100keV protons damage the junction ofthe cells to increase leakage current.PC1D program can not given the model of thejunction area.